全文获取类型
收费全文 | 7192篇 |
免费 | 342篇 |
国内免费 | 429篇 |
专业分类
化学 | 3107篇 |
晶体学 | 67篇 |
力学 | 151篇 |
综合类 | 10篇 |
数学 | 123篇 |
物理学 | 4505篇 |
出版年
2024年 | 3篇 |
2023年 | 46篇 |
2022年 | 83篇 |
2021年 | 89篇 |
2020年 | 145篇 |
2019年 | 126篇 |
2018年 | 158篇 |
2017年 | 124篇 |
2016年 | 240篇 |
2015年 | 213篇 |
2014年 | 267篇 |
2013年 | 350篇 |
2012年 | 802篇 |
2011年 | 785篇 |
2010年 | 579篇 |
2009年 | 646篇 |
2008年 | 492篇 |
2007年 | 549篇 |
2006年 | 336篇 |
2005年 | 257篇 |
2004年 | 237篇 |
2003年 | 190篇 |
2002年 | 216篇 |
2001年 | 130篇 |
2000年 | 147篇 |
1999年 | 129篇 |
1998年 | 137篇 |
1997年 | 57篇 |
1996年 | 48篇 |
1995年 | 52篇 |
1994年 | 36篇 |
1993年 | 36篇 |
1992年 | 31篇 |
1991年 | 20篇 |
1990年 | 30篇 |
1989年 | 21篇 |
1988年 | 19篇 |
1987年 | 10篇 |
1986年 | 18篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 6篇 |
排序方式: 共有7963条查询结果,搜索用时 15 毫秒
991.
You-Cun Chen Guang-Xiang Liu Xiao-Ming Ren You Song 《Journal of Physics and Chemistry of Solids》2008,69(10):2445-2452
Four molecular solids consisting of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical and benzylpyridinium or benzylquinolinium derivatives with molar ratios of 1:1 (1-3) and 2:1 (4) have been prepared and characterized. In the crystals of 1 and 3, TCNQ− monoanions and the corresponding cations form segregated stacks, which are regular in 1 but irregular in 3. Instead of segregated stacks, TCNQ− monoanions in 2 form isolated π-dimers. In the crystals of 4, two crystallographic independent TCNQ species possess almost equal fractional negative charge (ca. −0.5). Two types of TCNQ species form a tetrad, these tetrads make a TCNQ stack with the pattern …BAAB…BAAB… along the crystallographic a-b direction. The magnetisms for 1-4 can be simply explained by the formation of singlet spin state. A broken symmetry approach in a density functional theory framework at the ub3lyp/6-31 g level was used to calculate the magnetic exchange constants in 1-4. The results qualitatively demonstrate the observed magnetic properties. 相似文献
992.
We propose a simple moiré method of visualizing electromagnetic force lines. The indicial equation is first derived for the tangent (or normal) curve to the electric field (or magnetic induction) around two parallel-line charges (or currents). The derived equation is then shown to have a one-to-one correspondence with that of the moiré fringe formed by two overlapped radial gratings. Since the tangent (or normal) curve to the electric field (or the magnetic induction) corresponds to the direction of the electric (or magnetic) force on a test charge (or current), the radial grating moirés can be used for the visualization of electric (or magnetic) force lines. 相似文献
993.
J.P. Velev P.A. Dowben E.Y. Tsymbal S.J. Jenkins A.N. Caruso 《Surface Science Reports》2008,63(9):400-425
Recent advances in thin-film deposition techniques, such as molecular beam epitaxy and pulsed laser deposition, have allowed for the manufacture of heterostructures with nearly atomically abrupt interfaces. Although the bulk properties of the individual heterostructure components may be well-known, often the heterostructures exhibit novel and sometimes unexpected properties due to interface effects. At heterostructure interfaces, lattice structure, stoichiometry, interface electronic structure (bonding, interface states, etc.), and symmetry all conspire to produce behavior different from the bulk constituents. This review discusses why knowledge of the electronic structure and composition at the interfaces is pivotal to the understanding of the properties of heterostructures, particularly the (spin polarized) electronic transport in (magnetic) tunnel junctions. 相似文献
994.
Raj Bali Anirudh Pradhan Hassan Amirhashchi 《International Journal of Theoretical Physics》2008,47(10):2594-2604
A model of a cloud formed by massive strings is studied in the context of the usual general relativity. This model is used
as a source of Bianchi type VI
0 massive with magnetic field and bulk viscosity. To get a determinate model, we assume that the expansion (θ) in the model is proportional to the shear (σ) and also the fluid obeys the barotropic equation of state. The behaviour of the models from physical and geometrical aspects
in presence and absence of magnetic field and bulk viscosity is discussed. 相似文献
995.
Makoto Nakanishi Yukiyasu Matsuno Jun Takada 《Journal of Physics and Chemistry of Solids》2008,69(1):49-54
The influence of composition on the structural ordering and magnetism in the VxNb1+yS2 system has been investigated by X-ray diffraction and magnetic measurements. Stoichiometric V1/3NbS2 did not exhibit the structural ordering of vanadium between the NbS2 layers. In the ordered structure, the vanadium composition deviated from the ideal value of to both higher and lower values, while the niobium composition was in the range of 0.05?y?0.18. Excess niobium, y>0, is thought to play an essential role in the structural ordering in this system. For samples with excess niobium and ordered structures, a magnetic transition was observed at 20-50 K, depending on the composition. The spontaneous magnetization of 3-5×10−3 μB/V atom is thought to be intrinsic to this system. The magnetization curves consisted of a constant and a proportional parts of the magnetic field, which correspond to the spontaneous magnetization and high-field susceptibility, respectively. The magnetization curves and the temperature dependencies of the high-field susceptibility were quite similar to those of the canted antiferromagnetic NiS2. A correlation between the structural and magnetic ordering is suggested. 相似文献
996.
S. Mollah Z.A. Khan D.K. Shukla M. Arshad Ravi Kumar A. Das 《Journal of Physics and Chemistry of Solids》2008,69(4):1023-1028
Polycrystalline bulk ferromagnetic insulating (FMI) Ln0.85Ca0.15MnO3 (Ln=Nd, Pr and Sm) samples are prepared by standard solid-state reaction route and characterized. Powder X-ray diffraction (XRD) data of the manganites show single-phase character. Existing theoretical models predict that the high temperature (T>θD/2, θD being the Debye temperature) dc conductivity (σdc) of these samples is due to adiabatic small polaron-hopping conduction. Greaves’ and Mott's variable range hopping (VRH) conduction mechanisms are not suitable to explain the σdc data at low temperature (T<θD/2). 相似文献
997.
Tomomi Kanazawa Kohei Ono Masashi Yamazaki Shiho Cho Fumiyoshi Takano 《Applied Surface Science》2008,254(23):7918-7920
We propose a reactive ion etching (RIE) process of an L10-FePt film which is expected as one of the promising materials for the perpendicular magnetic recording media. The etching was carried out using an inductively coupled plasma (ICP) RIE system and an etching gas combination of CH4/O2/NH3 was employed. The L10-FePt films were deposited on (1 0 0)-oriented MgO substrates using a magnetron sputtering system. The etching masks of Ti were patterned on the FePt films lithographically. The etch rates of ∼16 and ∼0 nm/min were obtained for the FePt film and the Ti mask, respectively. The atomic force microscopy (AFM) analyses provided the average roughness (Ra) value of 0.95 nm for the etched FePt surface, that is, a very flat etched surface was obtained. Those results show that the highly selective RIE process of L10-FePt was successfully realized in the present study. 相似文献
998.
A piece of tissue extracted from a chum salmon Oncorhynchus keta head was measured with time-of-flight secondary ion mass spectrometry (TOF-SIMS) in order to evaluate the distribution and composition of magnetic materials in the tissue, which may concern with geomagnetic navigation of long-distance migrating salmon. Several depositions of iron compounds were detected in the tissue by TOF-SIMS analysis. Comparing with total ion images providing a topological tissue structure, specific distribution of iron ion in the tissue was clearly shown. Higher magnification TOF-SIMS analysis revealed the existence of the aggregations of iron particles. Iron oxide clusters comprising many submicron particles were also detected in the tissue using scanning electron microscopy and X-ray analysis, suggesting the common existence of submicron-scale iron oxides in salmon heads. These results suggest that TOF-SIMS analysis is a valid method to clarify detailed structures and chemical properties of candidate magnetoreceptors in fish heads. 相似文献
999.
Rapidly solidified nanocomposite Nd9Fe77−xB14Tix alloys, consisting of magnetic Nd2Fe14B phase and soft magnetic phases, were investigated. The effect of titanium addition on the structure and magnetic properties was studied. It was found that 2–4 at% Ti addition leads to substantial increase of the coercivity and maximum energy product, maintaining the remanence unchanged. The highest properties: Jr=0.81 T, JHc=907 kA/m, (BH)max=99 kJ/m3, were achieved for the Nd9Fe73B14Ti4 alloy. This effect we attribute to the formation of fine and homogeneous grain structure and a change of the phase morphology in the Ti-containing alloys. The initial magnetization curve indicates a change of the coercivity mechanisms giving rise to pinning of domain walls, which is caused by reduction of the crystallite size. 相似文献
1000.
M. Duttine R.B. Scorzelli G. Cernicchiaro G. Poupeau N. Guillaume-Gentil 《Journal of magnetism and magnetic materials》2008,320(14):e136-e138
Obsidians from major Ecuadorian sources were analyzed by SQUID magnetometry and electron spin resonance (ESR). The association of these two techniques permits to differentiate obsidians from the sources of Cotopaxi volcano and from the Quiscatola and Mullumica–Callejones sources of the Chacana caldera, taking into account various parameters arising from the M vs. H cycles and the X-band ESR spectra. The analysis of 27 archeological samples coming from the prehispanic site of La Maná allowed us to infer that most of them come from the Mullumica–Callejones source. 相似文献